This study is designed to evaluate the efficacy of a protective environment (laminar air flow rooms) in the management of patients with hematologic disease undergoing marrow transplantation. Gut sterilization, skin cleansing and sterile diets will be utilized. Patients will be randomized into the LAF rooms or to a control group. The incidence of bacterial, fungal, protozoan and viral diseases will be compared in the two groups. The incidence and severity of graft-versus-host disease will also be analyzed in the two groups. Finally, the effect of ultraisolation on survival will be determined.